Die casting machine with controlled injection



Jan. 27, 1970 E. A. R. MACE DIE CASTING MACHINE WITH CONTROLLED INJECTION 6 Sheets-Sheet 1 Filed July 12, 19 7 PRESSlRE SOURCE PRESSURE SOURCE DIE CASTING MACHINE WITH CONTROLLED INJECTION Filed July 12, 1967 'Jan..27, 1970 EA. YR. MACE 6 Sheets-Sheet 2 PRESSURE SOURCE PRESSURE SOURCE Jan. 27, 1970 V E. A. R. MACE 3,491,827

DIE CASTING MACHINE WITH CONTROLLED INJECTION Filed July 12, 1967 6 Sheets-Sheet 3 z '6 79 /50 PRESSURE 73 SOURCE PRESSURE 6/ 3; 7

6 6/, RS8UR 53 5 some;

4. r Z: 4f 57 4 1; g f a 436 Jan. 27, 1970 E. A. R. MACE 3,491,327

DIE CASTING MACHINE WITH CONTRQLLED INJECTION 6 Sheets-Sheet 4.

Filed July 12, 1967 Jan. 27, 1970 A 3,491,827

DIE CASTING MACHINE WITH CONTROLLED INJECTION Filed July 12, 19s? 6 Sheets-Sheet 5 I Jan. 27, 1-970 E. A. R. MACE 3,491,827

DIE CASTING MACHINE WITH CONTROLLED INJECTION Filed July 12, 1967 6 Sheets-Sheet 6 United States Fatent O 3,491,827 DIE CASTING MACHINE WITH CONTROLLED INJECTION Eric Arthur Roy Mace, London, England, assignor to Die Casting Machine Tools Limited, London, England,

a British company Filed July 12, 1967, Ser. No. 652,930 Claims priority, application Great Britain, July 12, 1966, 31,245/66, 31,300/66; Sept. 6, 1966, 39,791/66 Int. Cl. B22d 17/ 04 US. Cl. 164-318 Claims ABSTRACT OF THE DISCLOSURE A small die casting machine, having a piston and cylinder assembly moving the injection plunger, in which the inlet or outlet fluid flow for the cylinder is restricted during the early stages of injection to allow air to escape from the die cavity and is freer thereafter to accelerate the plunger and give a sharp casting.

This invention relates to die casting machines having dies forming a die cavity and a plunger which is movable (for example: by means of a fluid-operated piston and cylinder assembly) to inject casting material into the die cavity.

One of the problems in die-casting is to ensure that the casting material flows into thin section portions of the die cavity. It is known that air entrapped in the cavity causes difficulty in making castings with thin sections since the air can prevent the metal completely filling the cavity. The problem is particularly acute in small diecasting machines since the time taken for the plunger to inject the material into the die is extremely short in such machines; in many cases, it is insufficient to allow the air to escape from the die via the air vents which are normally provided for this purpose.

It is therefore the object of the present invention to provide an improved die-casting machine and an improved method of die casting, with particular reference to small machines.

The method of die-casting contemplated by the present invention essentialy consists in advancing the plunger to effect injection of casting material relatively slowly at first until the die is partially filled and subsequently advancing the plunger at a relatively faster rate to ensure that the casting material properly fills all the cavity. With this manner of operation, the relatively slow initial movement of the plunger gives sufiicient time for most of the air entrapped in thin section portions to be ejected out of the cavity while the final, faster rate of injection ensures that the material is finally injected into the cavity with a force sufficient to ensure that the material fills all the cavity and thereby produce a sharp casting.

The plunger is conveniently movable by means of a fluid operated piston and cylinder assembly. In general, there are two main ways in which the change in plunger speed may be effected. Where the piston and cylinder assembly is hydraulically actuated, the inlet pressure may be initially restricted by providing only a throttled flow of inlet fluid, the flow being suddenly increased at a suitable time. This method is also suitable for pneumatic operation, with which there is the further possibilty of providing an initial restriction on the exhaust fluid from the cylinder. All these are included Within the scope of the invention.

In the following, reference will be made to the accompanying drawings, in which:

7 FIGURE 1 illustrates a die-casting machine constructed in accordance with the present invention;

FIGURES 2 and 3 illustrate the die-casting machine of FIGURE 1 in different phases of a die-casting cycle;

FIGURE 4 is a simplified illustration of another diecasting machine constructed in accordance with the present invention;

FIGURES 5 and 6 illustrate a detail of the machine of FIGURE 4 and show different phases in a die-casting cycle;

FIGURE 7 illustrates, to a larger scale, a detail of the die-casting machine of FIGURES 4 to 6; and

FIGURE 8 illustrates another die-casting machine constructed in accordance with the present invention.

The three machines shown in FIGURES 1 to 3, 4 to 7 and 8 have, at least as far as conventional features are concerned, many details in common and it will be appreciated throughout the following that the application of like reference numerals to like parts indicates a like construction and function. The conventional features of a die-casting machine will be described in detail only with reference to FIGURE 1.

FIGURE 1 shows one embodiment of a die-casting machine constructed in accordance with the present invention, the machine in FIGURE 1 being at the start of an injection cycle before the injection of casting material is effected. The main parts of the machine comprise a piston and cylinder assembly 10 for effecting movement of a plunger 11 into a well 12 which is or has been filled with molten die-casting material. Downwards movement of the plunger 11 into the well 12 forces the material in the well up a goose-neck passage 13 through a nozzle 14 into a die cavity 15 formed when a fixed die plate 16 and a movable die plate 17 have been closed together. The construction of die cavities has been known for many years in the art and for convenience will not be repeated here. It is usual to provide air vents (not shown) leading away from the die cavityv 15 in order that air entrapped when the dies are closed may leave the die cavity when injection of the material from the well 12 is effected. After the die cavity is completely filled, it is conventional practice to withdraw the plunger 11 upwardly, subsequently break the the casting seal by an initial separation of the die plates, finally separate the die plates completely and eject the casting from the die cavity.

In FIGURE 1, molten metal 18 for the casting is retained in a reservoir 19, the reservoir being replenished at intervals in accordance with the usual practice. The well 12 is retained in a central bush 20 near the centre of the reservoir 19 and a port 21 communicates between the reservoir 19 and the port 22 in the side of the well 12 so that when the plunger 11 is withdrawn to an upper position after injection, casting material may flow from the reservoir 19 to fill the well again. In accordance with usual practice, the machine is tilted so that the height of material in the goose-neck passage after the well has been filled is as low as possible.

Secured to the reservoir 19 is a frame 23 holding a sleeve 24 in which is movable a connecting rod 25 which at its lower end is connected to the plunger 11. The connecting rod 25 is formed in two main parts, an outer part 25a and an inner part 2511. The part 25b is attached to the plunger 11 and is retained within the hollow lower portion of the part 25, being retained within the portion 25a by a crosspiece 26, provided at its upper end.

The part 25a is attached by means of the screw threaded link 28 to the piston 29 which is movable within a cylinder 30. The piston itself is reduced at its upper end, a reduced part 35 engaging a circular central recess in a circular plate 36, the plate 36 and the piston 29 retaining between them a flanged annular sealing ring 37 whose outer flange is a close sliding fit within the cylinder 30. At the lower end of the cylinder is provided an outlet port 31 leading to a conduit shown diagrammatically by a line 32. The other end of this conduit leads to an exhaust port whose configuration will be described hereinafter.

Provided on the link 28 is an L-shaped arm 33 which, when the piston 29 has partially completed its downward travel, operates a microswitch 34 whose function will be made apparent hereinafter.

Above the cylinder 30 is an assembly 38 which controls the inlet and outlet fluid from the cylinder. A body 40 of generally cylindrical form has two end chambers 41 and 42 and an inner chamber 43 of larger diameter than the end chambers. At each end of the inner chamber 43 there are two annular bushings 44 and 45 which mount for sliding movement through the body 40 a spool valve 46. The spool valve is shorter than the length of the body portion 40 and has two outer relatively thicker portions 47 and 48 and an inner portion 49 of like thickness, the thicker portions being separated by thinner connecting portions 50 and 51. The chamber 43 is divided into five approximately equal subchambers (43a to 432') by the five I-section double sealing rings 52. These have a diameter such that the outermost portions of their flanges are a close fit within the chamber 43; and the webs of the rings 52 have an inner diameter such that the thicker portions of the spool valve 46 are sealingly slidable from side to side in the rings 52.

Communicating with the left-hand end chamber 42 is a pilot port 53a supplied with pressure through line 53b from a fluid pressure source 53 when the source is actuated by a switch shown diagrammatically at 54. Application of fluid pressure to the pilot port 530 causes movement of the spool valve 46 in a rightwards direction. Likewise, there communicates with the right-hand end chamber 41 a pilot port 55 which may be supplied via line 56 with fluid pressure from a source 57 when the source is actuated by a switch 58. The application of fluid pressure from the source 57 to the port 55 effects leftwards movement of the spool valve 46. In the example shown in the drawings, the sources 53 and 57 are pneumatic sources and the switches 54 and 58 are manually operated switches. The middle sub-chamber 430 is permanently supplied with pressure from the source indicated diagrammatically at 59 via pipe 60 and the port shown at 61. The left-hand sub-chamber 43a communicates with the atmosphere by a port 64. The fourth chamber 43d includes a port 65 which leads to the conduit 32. Finally, the right-hand sub-chamber 432 communicates with an exhaust port 62 which leads to a conduit 63.

The conduit 63 leads to an assembly 66 which controls the flow of exhause gas from the cylinder 30. In this embodiment, the flow of exhaust gas is to be restricted until the die cavity is partly filled and relatively freer thereafter. Although this could be effected by using an adjustable orifice it is more convenient to provide two separate exhaust passages with a valve movable to select the relatively freer passage when the die cavity is partly filled. The assembly 66 embodies this form of control. It comprises a body 67 which is similar in construction to body 40, being divided into sub-chambers 68, 69 and 70 and end chambers 71 and 72 in a similar manner. In the body 67 is slidable a spool 73 whose thicker portions are a sealing fit within the sealing rings. The conduit 63 leads to the middle sub-chamber 69. The right-hand subchamber 70 leads to atmosphere via a relatively wide exhause port 74, whereas the left-hand sub-chamber 68 leads via conduit 75 to an adjustable needle valve 76 and an exhaust port 77.

The spool 73 carries at its left-hand end a ferromagnetic portion 78 constituting an armature for a solenoid shown diagrammatically at 79. The solenoid is actuated by the microswitch 34 to move the armature 78 and spool rightwards, the spool 73 being movable by means of fluid pressure applied to port 80 to return to the extreme leftwards position shown in FIGURE 1.

Other forms of actuation are possible, provided that they incorporate a member movable by or in accordance with the plunger, co-operating with an actuator in a fixed position to operate the valve spool 73 when the plunger 11 has partly filled the die cavity. There may be, for example, a pneumatic or hydraulic valve operable to apply fluid pressure to move the valve spool rightwards.

The manner of operation of the die casting machine shown in FIGURE 1 is as follows.

With the machine at rest at the beginning of a cycle, the piston 29 is at the top of the cylinder 30 with the exhaust port 64 open and with the air supply, which is permanently attached to port 61, being transferred via the inner annulus of the valve spool 46 to the port 65 and then through conduit 32 to the port 31 to hold the piston 29 at the upper end of the cylinder 30. At this time, casting material from the reservoir 19 will have filled the well 12. The casting cycle commences with the operation of switch 54 to cause the pressure source 53 to apply pneumatic pressure to the pilot port 5312 to transfer the valve spool 46 in a rightwards direction to the position shown in FIGURE 2.

When the machine is in the position shown in FIG- ure 2, air is transferred from the port 61 via the annulus in valve spool 46 through the port 81 in the top of the cylinder 30. This applies pressure to the front face of the piston 29 and the piston now starts to descend to force the material in the well 12 up the goose neck passage 13.

The exhaust from the cylinder is transferred via the port 31 and the conduit 32 and through parts 65, 43d, 43e, 62, 63, 69 and 70 to the conduit 75. During the initial part of the injection cycle, the valve spool 73 is in its extreme left-hand position so that the exhaust from the cylinder 30 is transferred only through the restricted outlet passage via the needle valve 76 and port 77. Accordingly, during this part of the injection cycle the movement of the piston 29 is relatively slow, the actual rate of movement being determined by the position of the adjustable needle in valve 76.

The slow movement of the piston continues until it is moved approximately half way down the cylinder. At this time the arm 33 operates microswitch 34 (which stays operative for the remainder of the injection stroke) to provide a signal to operate the solenoid 79. Of course, suitable current amplifying arrangements may be incorporated in order that the solenoid may be energized with suflicient current but such amplifying arrangements have not been shown since they will readily be appreciated by those skilled in the art.

When the microswitch 34 and accordingly the solenoid 79 is operated, the valve spool 73 is transferred to its extreme right-hand position. This position, now shown in FIGURE 3, changes the path of the exhaust from the cylinder 30 to the relatively free exhaust port 74 (since now chamber 69 can communicate with chamber 70). Since the inlet pressure to the cylinder is the same the piston moves at a greatly increased rate for the remainder of its downward travel.

During the initial relatively slow movement of the piston and the plunger there Will have been sufficient time for air in small parts of the die cavity to escape through the conventional air vents. However, during the latter, relatively faster movement of the piston and plunger the casting material is injected into the cavity with a greater force and thus it properly fills all the thin section portions of the die cavity.

When the casting is complete and it is desired to withdraw the piston and plunger the valve spool 46 is moved to its left-hand position, (FIGURE 1), the switch 58 being operated to apply inlet pressure to the port 55 for this purpose. Then the air from the air supply 59 is transferred to the lower face of the piston (via port 31) which is thereby drawn up to its uppermost position of FIGURE 1. At the same time, the exhaust from the outer face of the piston is via the port 81 and the exhaust port 64.

As the piston rises arm 33 disengages from switch 34 to release the spool 73 to its original position.

Reference will now be made to FIGURES 4 to 7 which illustrate a die casting machine incorporating an alternative embodiment of the invention. The die casting machine of these figures is identical, as far as the parts below screw threaded link 28 are concerned, with the machine of FIGURES 1 to 3. However, the machine in FIGURES 4 to 7 employs a different inlet pressure control.

The machines shown in FIGURES 4 to 7 and 8 differ from that of FIGURES l to 3, in that, in place of restricting the exhaust from the cylinder 30, a valve member is disposed in an inlet duct to provide a throttled flow of fluid to the cylinder until the die cavity is partly filled. FIGURES 4 to 7 show an arrangement primarily intended for pneumatic operation and FIGURE 8 shows an arrangement primarily intended for hydraulic operation. Suitable modification, if necessary, would render them suitable for hydraulic and pneumatic operation respectively.

In FIGURE 4, there is shown leading from the outward end of the cylinder 30 the conduit 100 in which the valve spool 101 is located. The spool valve is secured to the upper end of piston 29 by means of the screw threading 101a and comprises a first relatively thick portion 102 that is only slightly thinner intermediate portion 103 connecting the portion 102 with a similar portion '104 whose function will be described in more detail hereinafter. The upper end of the conduit 100 is sealed by a conventional sealing ring 105 engaging the periphery of the upper portion 104.

Leading off the conduit 100 is the port 106 which is fed with pneumatic fluid pressure from the valve 107.

The valve is operative "by suitable conventional means (not shown) to supply pressure either to the port 106 or to the port 109 so as to lower and raise piston 29 respectively. The valve is supplied with pressure from a source indicated diagrammatically at 108. For convenience in the description of FIGURE 4 it will be assumed that the fluid pressure source is pneumatic but hydraulic operation' may equally well be selected.

The downward (injection stroke) phase of operation of the die casting machine of FIGURE 4 is as follows.

The valve 107 admits fiuid into the port 106 and into the cavity formed in the conduit 100 between the portions 102 and 104 of the spool valve 101. Air cannot pass upwards owing to the seal provided by the sealing ring 105 but can only slowly enter the main cylinder 30 through the small clearance between the portion 102 and the inner face of the conduit 100. Thus the piston initially travels downward at a slow rate, alowing air trapped between the metal level and the die cavity 15 to escape through the aforementioned vents in the die cavity. The slow downward movement of the piston continues until the portion 102 of the spool valve 100 start to leave the passage 100 (FIGURE 5).

At this point, fluid will enter the cylinder 30 at a greatly increased rate, since portion 103 is narrower than portion 102, and since the reverse side of the piston will have had time to exhaust through the exhaust port 109 down to atmospheric pressure, the piston will travel downwardly at a high speed not only due to this equalisation of pressure but also due to the increase in fluid pressure provided by the increase of effective area of the inlet port which now essentially comprises the lower end of the conduit 100 with the intermediate reduced portion 103 of the valve spool within it.

When casting is completed, the piston has to be returned to its initial position. A great problem often encountered in die casting is the dripping of the molten metal in the nozzle onto the face of the cover half of the die. Torches may be applied to the nozzle to keep this metal molten so that when the metal in the cavity is solidified, that which is in the nozzle will remain fluid to allow flow of metal during the next shot. If this molten metal is not withdrawn from the nozzle, it will drip, when the dies separate, onto the faces of the dies. This would prevent the dies from closing completely during a a subsequent casting operation. The machine of FIG- URES 4 to 7 incorporate features directed to solving this problem.

It will be apparent that when the plunger 11 is withdrawn from the well 12, a vacuum is created in the goose neck passage 13 so that when the port 22 from the reservoir 19 is uncovered molten metal from the reservoir rushes up the goose neck passage and out through the nozzle to drip onto the fixed die plate as well as the metal already in the nozzle.

It will also be apparent that the plunger has to be withdrawn to draw away the casting material in the nozzle before the dies are open. Withdrawal of the plunger is normally effected by applying pressure from the valve to the exhaust port 109 and it will be appreciated that if the port from the reservoir is uncovered before the dies are separated (to destroy the partial vacuum in the goose neck) the goose neck will be substantially filled with casting material and the aforementioned "dripping will occur. The machine shown in FIGURES 4 to 7 ensures that there will be suflicient time to open the die cavity before the port 22 from the reservoir is uncovered. This is essentially achieved by providing an initial fast rate of withdrawal of the plunger 11 (to ensure proper withdrawal from the nozzle of the molten metal) and then slowing down, but not stopping, the plunger up to when the die plates have been opened.

FIGURE 6 shows in detail the upper part of the piston and cylinder assembly of the machine of FIGURE 4-. The upper end of the conduit is flanged to provide a generally circular table on which is mounted a hollow cylinder 110 containing oil 111. Over the passage 100 is formed the well 112 into which the valve spool end portion 104 extends. The well 112 is formed with a lower part of somewhat greater cross-section than the portion 104 but has a shoulder 113 defining an upper part 114 of the Well in which the portion 104 is a slidingly sealing fit. At the top of the well, and as more particularly shown in FIGURE 7, thereis an exhaust passage 115 with a needle valve 116 adjustable in position by means of the screw threading 124 engaging a co-operating threading in the body of the well;

During the slow down of movement of the piston a partial vacuum will be left in the upper portion of the well. This partial vacuum is relieved when the valve spool portion 104 leaves the shoulder 113, the oil in the reservoir entering the well by means of the port 117 to fill the well completely.

Referring particularly to FIGURE 6, when pressure is applied to the exhaust port, the piston will start to return in an upward direction at high speed. This will ensure that the injection plunger, which is normally a Nitralloy sleeve immersed in molten zinc (casting material) will not seize. The valve spool 101 will likewise travel rapidly upwards through the conduit 100 until it starts to enter the upper portion of the well 112. It has already been explained that during the injection phase of the casting cycle the well has been filled with oil from the reservoir (cylinder 110) through the port 117 provided. The initial upward rapid movement of the plunger withdraws all the casting material from the nozzle. When the portion 104 reaches the shoulder 113 in the well 112 the movement of the valve spool 101 and accordingly the piston 29 and plunger 11 will slow very substantially since oil from the upper part 114 of the Well 112 can only escape very slowly through the passage 115 which is controlled by the needle valve 116. The needle valve 116 is adjusted so that the port 22 is not uncovered until the dies have started to open. The opening of the die cavity destroys the vacuum which is normally present and accordingly by the time the plunger 11 uncovers the port 22 from the reservoir 19 the vacuum in the goose neck passage 13 has been destroyed by the opening of the die cavity and the metal in the goose neck will not rise and refill the nozzle 14.

It will 'be apparent that a valve member similar to that shown in FIGURES 4 to 7 could be provided in the machines shown in FIGURES 1 to 3 or 8 as a separate extension on the connecting rod between the piston and the plunger. Such an arrangement has not been shown for convenience.

In FIGURE 8 is shown a die casting machine incorporating yet another embodiment of the invention.

The machine shown in FIGURE 8 is intended for hydraulic operation only. The details of the machine as far as the plunger 11, reservoir 19 and die cavity are concerned are the same as those described with reference to FIGURES 1 and 4. In FIGURE 8, the piston 129 is slidable in the cylinder 130. At the inlet end of the cylinder is a port 131 leading to a transverse passage 132 communicating via a duct 133 with an inlet control valve 134. Aligned with the piston 129 is a further piston 135 movable in a cylinder 136 formed on the body 138. A rod 137 extends from the piston 135 through a port (not referenced) towards an extension 141 on piston 129. The ports between the cylinders 130 and 136 are sealed from the transverse passage 132 by the sealing rings 139 and 140, which are close fits around the rod 137 and'extension 141.

Arranged transverse the passage 132 is a valve spool 142 movable in a passage 143. The valve spool is attached by means of a lost motion linkage to the piston 129. A bar 144 extends outwardly from port 25, the bar receiving the rod 145, which has an adjustable stop 146 and is connected to valve spool 142. By-passing the valve spool 142 is a bleed passage 147 containing a needle valve 148.

At the start of an injection cycle, oil under pressure is transferred to theinlet port 149 in the valve 134. At this time, valve spool 150 in the valve 134 is located so that the duct 133 is open to the oil. The oil is transferred to-the passage 132 which is blocked by the valve spool 142. The inlet oil thus traverses the passage 147 via the needle valve 148 to the left-hand end of the passage 132, and through port 131 to move the piston 129 slowly downwards, The die cavity 15 will be filled at a relatively slow rate. The needle valve 148 is adjustable so that the slow forward movement of the piston may be at an adjustable rate.

The piston 129 will continue to move downwards slowly until the bar 144 strikes the adjustable stop 146, which will be carried along with the bar 144 and will therefore move the rod 145 to open the passage 132. It will be readily apparent that spool valve 142 and its passage must be designed and arranged to ensure that passage 132 remains open for the rest of the injection stroke. Oil at inlet pressure will thereby be transferred through port 132 into the cylinder 130 to move the piston 129 downwards at high speed. The piston will travel forward at this high speed for the remaining part of the injection stroke, thus, as in the previously described embodiments, ensuring a sharp casting.

Since the pressure in a hydraulic system with a free moving piston is below the inlet pressure, the pressure in the left-hand end of the passage 132 will be below the pressure applied to the inlet port 149. It follows that since the pipe 151 is restricted by needle valve 152 there will be a slight pressure drop between passage 132 and duct 133. When the dies are almost completely filled and the piston tends to stop there will then be a sharp rise in the oil pressure in the passage 132 and the pressure at port 153 will increase. The spring loaded needle valve 154 only opclL Whsin the pressure in the pipe 151 is approximately of the normal line inlet pressure at 149 so that when the pressure in passage 132 rises sharply oil is transferred via port 153 to push valve spool 150 to close passage 133 to the inlet pressure and open duct 156 to the inlet pressure. The main oil sup-ply is now transferred to the rear of piston which will travel forwards rapidly, its rod 137 sealing the passage 132. The rod 137 strikes the extension 141 of piston 129 and since the cross-sectional area of the piston'rod 137 is considerably less than the area of the piston 135 the pressure exerted on the piston 129 will be increased. Preferably the ratio of the areas of the rear piston 135 and rod 137 is approximately 3 to 1 so that, using a typical line pressure at 1500 lbs. p.s.i. the pressure of the rod 137 on the piston 129 will be stepped up to 4500 lbs. p.s.i. This will provide a sharp increase of injection pressure to ensure a sharp casting.

I claim:

1. A die casting machine having dies forming a die cavity, a nozzle for the injection of material in the cavity a plunger movable to force material through said nozzle, a piston connected to the plunger and movable to cause injection of material when fluid pressure flows from a pressure source through an inlet duct to a cylinder in which the piston moves, a valve member in said inlet duct, said valve member having means to provide a throttled flow of fluid through said inlet duct during an initial period of injection and being actuated by the movement of the piston and plunger to provide a relatively freer fluid flow through said inlet duct when the plunger has partly filled the die cavity, said valve member having means to initially block the inlet duct and means including a restricted orifice, for providing a fluid by-pass, the valve member being connected through a lost-motion linkage to the plunger and piston.

2. A die casting machine as claimed in claim 1 wherein the restricted orifice comprises an adjustable valve.

3. A die casting machine as claimed in claim 2 wherein the fluid source is hydraulic.

4. A die casting machine having dies forming a die cavity, a nozzle for the injection of material into the cavity, a plunger movable to force material through said nozzle, a piston connected to the plunger and movable to cause injection of material when fluid pressure flows from a pressure source through an inlet duct to a cylinder in which the piston moves, a valve member in said inlet duct, said valve member having means to provide a throttled flow of fluid through said inlet duct during an initial period of injection and being actuated by the movement of the piston and plunger to provide a relatively freer fluid flow through said inlet duct when the plunger has partly filled the die cavity, a further piston and means, responsive to the increase of pressure in the cylinder to cut off fluid flow to the inlet duct and redirect the fluid flow from the source to move the further piston to strike the first piston thereby to provide a sudden increase in injection pressure.

5. A die casting machine as claimed in claim 4 wherein the pressure source is hydraulic, and a passage is provided to lead from the inlet duct, to a spring loaded valve, said last named valve being opened by the increase in the hydraulic fluid in the duct, and being thereby directed to move a further valve to out 01f fluid to said inlet duct and to effect the redirection of the fluid flow.

References Cited UNITED STATES PATENTS 2,618,292 11/1952 Ring 164315 X 2,958,104 11/1960 Ohse 164315 X 2,494,071 1/1950 Veale 164-315 ROBERT D. BALDWIN, Primary Examiner US. Cl. X.R 164-315 

